1. Field of the Invention
The present invention relates an apparatus and a method for lapping magnetic heads, and in particular to an apparatus and a method for lapping a workpiece provided with a plurality of magnetic heads supported by a tool.
2. Description of the Related Art
Conventionally, a thin film magnetic head, which is used in a disc drive in a computer, is manufactured in a batch process. In this process, a workpiece, provided with a ceramic bar (thereafter being divided into sliders) on which a row of transducers including a plurality of thin film magnetic heads are arranged, is lapped such that throat heights in gaps of the respective transducers are adjusted to have desired values at which optimum data signal processing can be realized.
A problem that exists in lapping such magnetic heads so as to obtain desired throat heights is that the ceramic bar or the workpiece is stressed and/or has an undesirable curvature or bow. Namely, when the ceramic bar is stressed and/or has an undesirable curvature or bow, a lapping apparatus can not uniformly lap the ceramic bar. For example, even if the throat heights of the magnetic heads on a center of the ceramic bar have optimum values, the throat heights of the magnetic heads on both ends of the ceramic bar might be too low or too high to have optimum values.
An apparatus for lapping magnetic heads, which can solve such problem, is disclosed in U.S. Pat. No. 5,620,356. A ceramic bar is adhered to a bottom of a tool, which likes a long thin plate. The apparatus adjusts throat heights of thin film magnetic heads arranged on the ceramic bar to be optimum by correcting the curvature of the ceramic bar and lapping the corrected ceramic bar while measuring resistances whose values are changed by the throat heights.
In the lapping apparatus disclosed in the U.S. patent, the curvature of the ceramic bar is corrected by applying loads in up and down directions to three portions of the tool provided along the longitudinal direction of the tool. The applied loads are changed in accordance with the abrasive amount of the magnetic heads obtained by resistances changed by the throat heights.
The throat heights of the magnetic heads need to be lapped with higher accuracy in the feature. However, as mentioned above, the lapping apparatus disclosed in the U.S. Patent applies loads in an up and down direction to three portions of the tool provided along the longitudinal direction of the tool. The lapping apparatus therefore can only deform the ceramic bar into such a shape that is approximated by a fourth order curve. As a result, shape patterns of the throat heights of the values of the magnetic heads to be lapped are limited to curves, which are approximated by a fourth order curve or a less than fourth order curve.
On the contrary, the distribution of values of the throat heights of the ceramic bar lapped by a conventional lapping apparatus actually has a complicate shape pattern such as a shape pattern which is approximated by a sixth order curve or a more than sixth order curve. The conventional lapping apparatus therefore can not correct the throat heights with accuracy in the case that the distribution pattern of the throat heights has such complicate shape pattern.
FIG. 28 shows a distribution of values of throat heights of the ceramic bar along a longitudinal direction of the bar when a conventional lapping apparatus laps a 50 mm long ceramic bar by automatically controlling throat heights of the bar. In FIG. 28, a solid line is a sixth order curve showing a distribution pattern of values of the throat heights of the bar, and a broken line is a fourth order curve showing a distribution pattern of values of the throat heights of the bar. As clearly shown in FIG. 28, the actual distribution pattern of values of the throat heights of the bar can be accurately approximated by the solid line of the sixth order curve.
As mentioned above, the actual distribution pattern of the values of the throat heights of the bar can be approximated by a sixth order curve or a more than sixth order curve. On the contrary, shape patterns of the throat heights of the magnetic heads to be lapped are limited to curves which are approximated by a fourth order curve or a less than fourth order curve when using a conventional lapping apparatus. Therefore, as show in FIG. 28, the conventional lapping apparatus can not correct portions having distribution pattern of the throat heights of the bar which are only approximated by high order curves.
Accordingly, the conventional lapping apparatus can not correct the throat heights of the ceramic bar with accuracy if the throat heights of the magnetic heads need to be lapped with higher accuracy.
It is therefore an object of the present invention to provide an apparatus and method for lapping magnetic heads which can accurately correct a curvature or bow of a workpiece.
It is another object of the present invention to provide an apparatus and method for lapping magnetic heads which can accurately correct a curvature or bow of a workpiece in accordance with a distribution pattern thereof.
The above objects are achieved according to the present invention by providing an apparatus for lapping a workpiece including a plurality of magnetic heads supported by a tool, the apparatus comprising a rotary lapping table having an abrasive surface, a lapping device assembly provided so as to be movable with respect to the abrasive surface of the lapping table, the lapping device assembly including means provided at a lower portion of the lapping device assembly for supporting the tool and means for respectively applying predetermined loads to a plurality of load applying portions of the tool, the load applying portions of the tool being disposed along the longitudinal direction of the tool, and the load applying means applying the loads from a plurality of different directions to at least one of the load applying portions of the tool so that the tool is deformed into a predetermined shape.
In a preferred embodiment of the present invention, the load applying means has means for applying a vertical load to at least one of the load applying portions of the tool.
In a further preferred embodiment of the present invention, the load applying means has means for applying a horizontal load to at least one of the load applying portions of the tool.
In a further preferred embodiment of the present invention, the load applying means has means for applying a rotating load to at least one of the load applying portions of the tool.
In a further preferred embodiment of the present invention, the tool supporting means supports the tool at about a longitudinal center portion of the tool.
In a further preferred embodiment of the present invention, the lapping device assembly further includes means for tilting the lapping device assembly about a tilt shaft parallel with the abrasive surface.
In a further preferred embodiment of the present invention, the apparatus further comprises means for oscillating the lapping device assembly in a predetermined angle.
The above objects are also achieved according to the present invention by providing a method for lapping a workpiece including a plurality of magnetic heads, the method comprising the steps of providing a tool for supporting the workpiece, a rotary lapping table having an abrasive surface, and a lapping device assembly provided so as to be movable with respect to the abrasive surface of the lapping table, said lapping device assembly including means provided at a lower portion of the lapping device assembly for supporting the tool, attaching the tool to the tool supporting means of the lapping device assembly, the tool having a plurality of load applying portions disposed along the longitudinal direction thereof, and lapping the plurality of magnetic heads of the workpiece by applying the loads from a plurality of different directions to at least one of the load applying portions of the tool so that the tool is deformed into a predetermined shape.
In a preferred embodiment of the present invention, the lapping step includes the step of applying a vertical load to at least one of the load applying portions of the tool.
In a further preferred embodiment of the present invention, the lapping step includes of the step of applying a horizontal load to at least one of the load applying portions of the tool.
In a further preferred embodiment of the present invention, the lapping step of includes the step of applying a rotating load to at least one of the load applying portions of the tool.
In a further preferred embodiment of the present invention, the tool supporting means supports the tool at about a longitudinal center portion of the tool.
In a further preferred embodiment of the present invention, the method further comprises the step of tilting the lapping device assembly about a tilt shaft parallel with the abrasive surface.
In a further preferred embodiment of the present invention, the method further comprises the step of oscillating the lapping device assembly in a predetermined angle.
The above and other objects and features of the present invention will be apparent from the following description by taking reference with accompanying drawings employed for preferred embodiments of the present invention.